Cory: how many plecos do you have? If you only have one, I would suggest getting another one so that the one you have may be happy. Maybe the one you have is not happy being alone, if he is the only pleco you have. It could be why he isn't eating anything.
Plecos eat what is left over from what other fish don't eat, plus they eat fish waste as well. My 55 gallon tank is clean and clear, and I have two plecos that keep it that way.